Fin-keel catamaran

ABSTRACT

A catamaran type yacht is disclosed which is of very narrow overall beam, having an elongated fin-type keel adjustably mounted on the fore-to-aft center line between its dual hull sections; and this fin-keel is operated adjustably under the control of a simple manual retraction mechanism. The main or wing mast of the craft has means for pivotally mounting the same at a novel stepping sub-assembly; and the mainsail boom is connected to the mast by a gooseneck loop device which allows for a tilt at an acute angle to a vertical plane including the boom axis. Provision is also made for a vertical adjusting movement of the boom in a relatively limited degree. Each hull member is equipped with a pivotally mounted kick-up rudder, the rudders being coupled for conjoint tiller operation. A solid section forestay or job spar is employed in a novel procedure of facilitating raising of the main mast above its stepping unit; and a pop-top type cabin cover is provided for installation in small yachts, with a flexible tent auxiliary shelter operatively connected to the pop-top when the latter is erected.

United States Patent 1 Miller 1 FIN-KEEL CATAMARAN 21 Appl. No.: 177,930

52 us. c1. ..114/39,114/6l 511 rm. c1 B63 b 35/90 [581 rield'tfise'arcn;..1l4/39,665R,66SH,

114/127-140,144,149,l62165,89,90, 104,106,l07;9/1T' 1 Jan. 29, 1974Primary ExaminerDuane A. Reger Assistant Examiner-Jesus D. SoteloAttorney, Agent, or FirmWhittemore, l-lulbert & Belknap [57 ABSTRACTplane including the boom axis. Provision is also made' for a verticaladjusting movement of the boom in a relatively limited degree. Each hullmember is equipped with a pivotally mounted kick-up rudder, the ruddersbeing coupled for conjoint tiller operation. A solid section forestay orjob spar is employed in a novel procedure of facilitating raising of themain mast above its stepping unit; and a pop-top type cabin cover isprovided for installation in small yachts, with a flexible tentauxiliary shelter operatively connected to the pop-top when the latteris erected.

25 Claims, 27 Drawing Figures [56] References Cited 8 UNITED STATESPATENTS 2,991,749 7/1961 Patterson 114/162 3,077,850 2/1963 Beuby114/66.5 l-l 3,085,540 4/1963 Crabi11e.. 114/162 3,227,123 1/1966 Voigt9/1 T 3,575,124 4/1971 Alter 114/165R 3,507,240 4/1970 Butler 114/393,611,969 10/1971 Hood 114/106 2,794,192 6/1957 Paris 114/66.5 H2,858,788 11/1958 Lyman.... 114/39 3,014,674 12/1961 Strawn 114/66.5 H

W123 II ML C 44 46 PAIENIEIJJANZQIHH SHEEI 1 0F 8 INVENTOR.

REGINALD T MI BY m PMENIEI] JAN 2 9 I974 SHEET 2 OF 8 INVENTOR.

REGINALD T MILLER BY Lac I a /J -w;

PAIENIED JAN 2 9 I974 sum 3 or s INVENTOR.

REGINALD T MUL BY L4 6 41 M/%2%M I g f saw u nr 3 INVENTOR. REGINALD T.MILLER PAIENI JAN 2 9 1914 PAIENTED JAN 2 9 I974 SHEET 5 BF 8 INVENTOR.

EGINALD T MILLER PAIENTEUJANZSIQM FIG 23 REGINALD T MILLER PATENTEUJAN29I974 SHEET 8 BF 8 INVENTOR. REGINALD T MILLER FIN-KEEL CATAMARANBACKGROUND OF THE INVENTION.

1. Field of the Invention The refined design criteria for catamaran sailboats as outlined in the Summary of the Invention to follow, areapplicable to yachts of not only cruising size, e.g., 30-70 foot length,but also to small midget ocean racing class and lake sailors, since theengineering of such improvements for a midget ocean racing yacht is moredifficult than for larger yachts; the design of a small 21 foot M.O.R.C.is depicted herein in the expectation that it is the most instructive.

2. Description of the Prior Art A search reveals patents to Patterson,US. Pat. No. 2,991,794 of July 11, 1961, relating to a pivotally mountedhydrofoil or keel structure, as mounted amidships of a single keelcraft; and patents such as Dutcher, US. Pat. No. 1,408,868 of March 7,1922, showing mast and boom arrangements of a sort only most generallysimilar to the present improved gooseneck mast and boom couplingstructure. However, none of the pertinent prior art of which I am awarereasonably shows or suggests the structural arrangements and attendentadvantages described in the Summary, Specification and Discussion tofollow.

SUMMARY OF THE INVENTION The herein-presented improvements in the designof cruising catamarans are varied in nature, and have materially reducedor eliminated many drawbacks of the standard beam-catamaran relying uponyacht weight and beam for stability, and it is a fact that at a 65-75angle of heel the beam-catamaran will capsize. This primary problem ofstability has been eliminated in my improvement by its introducing along retractable fin-keel mounted along the center line of the bridge orwing area. The length of this fin-keel is about one-third of the LWL ofthe craft so that the ballast required to insure high efficiency is notexcessive. The long length of this fin-keel is not objectionable sinceit is easily retractable, on release of an associated safety mechanism,in case it should encounter a positive obstacle or strike the bottom, asin beaching. The readily adjustable nature of certain control mechanismsfor the finkeel allows for adjustment of the latter at any indicatedangle so the catamaran can in effect be tuned for sailing efficientlywithout a jib sail, as under heavy wind conditions. It can also beadjusted for shallow water situations, as for a beach departure.

The presence of this long fin-keel enables the overall beam of the yachtto be reduced from a normal 40 percent to 50 percent of the hull lengthto a minimum allowable before wave interference between the hullsintroduces excessive drag, namely 33 percent of the length of the hullmembers. This factor is important because it saves in overall yachtweight, since weight is a function of surface area. Reduced weightimproves speed. Narrow beam also signifies an expenditure of less energyto turn the yacht, and hence tacking ability is improved.

The improved finkeel catamaran has been designed with its twin hullstoed out one or two degrees, which has a beneficial effect when sailingto windward. With the weather hull flying, as is the normal sailingcharacteristic when beating to windward, the fin-keel assumes the properangle to eliminate lateral crab angle. Thus drag due to crab angleeffects is eliminated and efficiency is again improved.

A methematical analysis of the characteristics of a catamaran askeel-refined in this way shows an improved wind velocity vs. stabilitycurve from which it can be deduced that the fin-keel catamaran caneasily be sailed at 15 to 30 angles of heel, thus eliminating the dragof the weather hull and still giving rise to no fear of capsize.

To recapitulate:

1. Because of the positive restoring forces, even at large angles ofheel, capsize is eliminated.

2. Windward performance is improved because (a) skin friction drag isreduced 35 percent as the weather hull lifts (flies); (b) windage dragis reduced 10-30 percent because of a narrower hull design; (0)crab-angle drag is significantly reduced because lateral resistance iscarried by the efficient fin-keel, and not by the hulls, by reason oftheir being toed out, and (d) the narrow hull spacing requires lessenergy to turn, thereby improving tacking.

3. Narrow design also facilitates docking.

4. The pivoting fin-keel can be adjusted to any angle, so that (a)precise tuning of the sails or sail (if the main is used alone or isreefed) is possible while under way; (b) the all-up keel position allowsbeaching; (0) when maneuvering in shallow waters the fin-keel can beadjusted to the level of the draft of the hulls, and still provide theminimum lateral resistance needed for tacking; and (d) when running downwind and requiring no lateral resistance, keel drag may be eliminated byelevating the tin-keel to its all-up position, thus reducing overalldrag.

While the above discussed fin-keel and hull considerations are of majorimportance in a yacht according to the invention, the further mast, maststepping, mastboom coupling, rudder and other improvements, as shown andhereinafter described under special headings, are also considered to beof substantial novelty and merit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view in side or beamelevation generally illustrating the hull of the craft as equipped withvarious improved structural features of the invention referred to in theAbstract;

FIG. 2 is a very schematic stern elevational view of the boat outline ata angle of heel to starboard;

FIG. 3 is a view in top plan of the general hull and deck layout;

FIG. 4 is a fragmentary enlarged scale view in vertical section on line44 of FIG. 3, illustrating a novel mainsail track feature;

FIG. 5 is a beam elevation similar to FIG. 1, but more clearly showingthe general arrangement of a fin-keel enclosure trunk and a crank-typeoperating device for the keel;

FIGS. 6A and 6B are similar fragmentary views in vertical fore-to-aftcross section mid-beam of the craft, showing details of a safety releaseand retrieve mechanism for the keel, FIG. 6A representing a keel-latchedcondition prior to keel release and FIG. 6B depicting, in solid anddotted line, positions of the parts after release and retrieval of thefin-keel;

FIG. 7 is a schematic side elevation in very small scale of an upwardlytapered main mast pursuant to the invention;

FIG. 8 is an end or prow elevation of the mast outline of FIG. 7;

FIG. 9 is an enlarged scale fragmentary view in section on a linecorresponding to line 99 of FIG. 7, in which the nature of the mastconstruction is shown, along with associated halyard and batten featuresof the mainsail;

FIG. 10 is a schematic view in plan showing the nature of laminar airflow in relation to the mast and mainsail in different angularlycambered positions of the masts sail, also indicating different angulardispositions of the yacht axis in sailing;

FIG. 11 is a plan view illustrating details of a tiltably adjustableand'settable yoke or gooseneck boom-tomast connection which is of valuein tacking, optional horizontal and 45 angularly tilted settings of thegooseneck being indicated respectively in solid and dotted line in thefigure;

- FIGS. 12 and 13 are respectively fragmentary views in section onbroken section line 1212, and in elevation as viewed from line 13-13 ofFIG. 11;

FIG. 14 is a view in side elevation as partially sectioned vertically ina generally fore-to-aft plane, i.e., on the line 14l4 of FIG. 16,through one of the hull sections rudder trunk member, the viewillustrating specific rudder details in down and up positions of therudder blade proper, as in solid and dotted line, respectively',

FIG. 15 is a fragmentary side view of a portion of the rudder andencasing rudder trunkarrangement, being viewed from the cross-beamdirection of the line 15--l5 of FIG. 16;

FIGS. 16 and 17 are fragmentary upper and lower stern elevational viewsof the said arrangement, as viewed from the respective lines 1616 and17-17 of FIG. 14;

FIG. 18 is a view in fore-end elevation schematically illustrating aprocedure of mounting the main mast of the craft to a steppingsub-assembly or unit;

FIG. 19 is a fragmentary elevational view of a jib spar and jib reefingdrum sub-assembly;

FIG. 20 is a view in horizontal section on line 20-20 of FIG. 19;

FIGS. 21 and 22 are, respectively, fragmentary views in front and sideelevation of mast stepping structure details;

FIG. 23 is a schematic side view of the prow section of the craft, whichsupplements FIG. 18 in regard to the procedure of the raising of themast by operations performed on the jib spar;

FIG. 24 is a fragmentary beam-elevational view schematically depicting apop-top and tent unit as mounted to the superstructure of the boat;

FIG 25 is a fragmentary view in enlarged scale side elevationillustrating details of that unit; and

FIG. 26 is a fragmentary view in aft elevation, as from the line 26-26of FIG. 25.

DESCRIPTION OF A PREFERRED EMBODIMENT General Arrangements FIGS. 1, 2and 3 of the drawings show the dual hull craft of the invention as beingprovided with a pivotally mounted fin-keel, generally designated I,mounted medially between identical molded fiberglass port and starboardhull sections H of the craft; and twin rudders 2, one on each of saidsections. The latter are arranged not to toe outwardly from the fore andaft center line of the boat at a mild angle, as are the hulls, but areparallel and on the same parallel axis as the keel. FIG. 3 shows themild angle of toe-out of the hull members H divergently in relation tothe center line C/L of the craft to improve the windward sailingcharacteristic, as mentioned above. A hinged pop-top hatchway cover of apop-top designated 3, is shown in FIG. 1 as being upwardly swingablethrough a bit less than from 3. normal solid line cruising positionthereof to the position depicted in dotted line, at which a tent 4 maybe set up aft of it to shield the area behind the pop-top 3. The latterextends over somewhat more than half the starboard-to-port cabin area ofthe vessel.

FIG. 1 shows a roller reefing drum 5 as mounted fast at the lower end ofa solid-section jib spar 6, the spar and drum having a pivotal ball andsocket-type support at 6 at the bottom thereof; and a mast step 7 ismounted fixedly atop a curved deck panel P spanning and being integrallymolded with the hull members H above the wing area between the latter.

The reference numeral 8 generally designates the improved fiberglassmain wing mast pursuant to the invention, on which a special gooseneckunit 9 adjustably mounts the mainsail 10 at its boom 11.to the mast. Theboom is shown in solid line in FIG. 1 in the normal sailing position andin dotted line when raised for lifting of the pop-top 3 and erection oftent 4, as will be described. Full length battens 13 are applied to themain wing sail 10; and a main sheet pulley system 12, schematicallyshown, is conventionally employed. An apparent wind indicator 14 isfastened to the forward surface of mast 8, directly above a pivotal balland sockettype connection to the latter of the top of jib spar 6, as at6". This enables the captain to ascertain immediately and at any timewhether or not the mast 8 is oriented or tuned correctly to theprevailing wind condition. As indicated in FIG. 1, a lower bulge linel6, which defines the bottom of an elongated stabilizing bulge 24 on theouter side of each hull member H, is approximately mid-way between thegunwhale and keel line surfaces of said members.

The roller reefing drum 5 for jib spar 6 is rotatively mounted midwayalong the top of a forestay cross arm 17 spanning between the hullmembers H; and this arm also supports the forward margin of a Dacronstrapfabricated safety net 18 (FIG. 2). The crafts jib 19 is reefedeasily toward or to the shortened position thereof, shown in dotted linein FIG. 1, by rotation of the reefing drum 5, as through tensioning of aline 20 fixed to and wound about the drum, the line extending aft to thecockpit for convenient operation. .lib 19 is unreefed toward or to thefully spread position indicated in dot-dash line in FIG. 1 by tensioningjib-setting line 19' from the cockpit area, generally designated C.

Main mast side stays 21 normally attach downwardly to chain plates 21'fixed on hull members H, H; but temporary mast stays 22 will be employedduring stepping and raising of the mast 8 (FIGS. 18and 23), the stays 22being releasably snapped to another set of chain plates 22' more closelyadjacent the mast'step sub-assembly or unit 7.

The reference numeral 23 appearing in FIG. 1 generally designates acrank-wheel operated device (illustrated in detail in FIGS. 6Aand 6B)for elevating and lowering the fin-keel 1. FIG. 1 also shows in dottedline the beam profile of mast 8 at a full swing or 45 angle of trimcontemplated by the invention, the normal straight fore-to-aft profileappearing in solid line.

As viewed in plan in FIG. 3, in addition to jib spar, hull cross-arm andmast step features referred to above in a general way, the craft affordsa cabin space or hatchway just forward of the open cockpit C which spaceis normally covered by the pop-top 3; and the decks above-cabinstructure includes a slidable hatch 41 on the port forward side ofcockpit C, the latter being defined by upright siding 42. A curvedmainsail stay track 43 is fixed to an after deck D spanning and rigidlyconnecting (in coaction with the fore deck panel P) the hull sections H,extending across the deck aft of the cockpit; and tillers 44 coupled bya rugged cross arm 45 extend rearwardly over the respective hull membersH into rudder cages or trunks 46 pivotally hung aft of those members.The nature of the tiller and rudder sub-assemblies is illustrated inFIGS. 14-17, inclusive. Splash guards G protect the cockpits occupant.

FIG. 4 shows structural details of the mainsail track 43 to include anupright track core formation 47 integrally molded as part of the hulldeck D, projecting at 90 to the upper surface of the latter. Stainlesssteel straps 48 are riveted on opposite sides of the core 47, extendingthe entire length of track 43; and an inverted U-shaped mainsail trackcarriage 49 of the pulley system 12, appearing in dotted line in FIG. 4,rides the track, as guided by anti-friction rollers 50 beneath thestraps 48, the rollers being pivotally mounted internally of parallellower legs of the carriage 49.

FIN-KEEL AND I-IULL CONSIDERATIONS FIG. 2 shows the catamaran hull at a90 angle of star-board heel, indicating how the position of an externalhull bulge 24 on each hull section above the line 16 affords variousoperational improvements in consequence of and in conjunction with thekeel features. In this view, the effective overall tin-keel length L isto be considered to be one-third of the load water line length of thehull, being instanced as 7 feet; and the hull separation S betweencenter lines of the hull members H will be considered to be the same,i.e., 7 feet for hulls 21 feet in length. Lead ballast 27 at the foot ofkeel 1 is minimal for needed stability due to the length of fin keel l.The center of mass C/M of the craft, being located as designated in FIG.2, then acts on a lever or moment arm of length M from a center ofbuoyancy C/B shown as being on a line normal to the keel l and waterline WL when the craft is at an extreme 90 heel angle. The relationshipof the load water line WI, under a normal static condition is indicatedin dotted line in FIG. 2.

Thus, it is seen that the hull bulge 24 improves the position of thecenter of buoyancy C/B; the restoring moment arm force couplerepresented by the product of mass at C/M times moment arm is maximized.Bulge 24 also obviously reduces spray into the cockpit C and imparts abeautiful line to the hull, giving the illusion of a longer one ofenhanced eye appeal. Other more significant features of advantage havebeen enumerated in the preceding Summary.

FIN-KEEL ADJUSTMENT FIG. 5 shows the hull structure of craft to includea fin-keel centerboard trunk 51 located mid-way between the hullmembers, from which trunk the keel 1 pivotally depends, and at which thekeel is adjusted as to its fully extended angular position appearing insolid line or any intermediate position between that and a fullyretracted position (dotted line). Parallel afterbrackets 52 are rigidlyattached to the walls of keel trunk 51 for a purpose to be described.

The profile line of the starboard hull H and section of the wing memberappears at 54 in FIG. 5, the port section line being the same. Theforestay cross arm 17 attaches rigidly between these hull members nearthe upper prow apex thereof, as indicated in that figure.

Reference being had to FIGS. 6A and 6B for specific details, said trunk51 is internally recessed from its rear to house the arcuate top of keelI; and a safety release latch arm 56 pivotally mounted between the trunkwalls is releasably engageable forwardly with a latch detent formation56' on the keel top. Arm 56 is resiliently urged counterclockwise forthis engagement by means to be described; and a rubber shock absorberpad 57 is fixedly applied to the aft upper keel portion, directly to itsrear, the pad normally, in the sailing position shown in FIG. 6A,rearwardly abutting an operating part to be described. Under anysignificant positive aft-wise pressure on keel 1 the latch 56 will yieldand lift so that the keel can swing free and avoid damage.

Keel 1 is mounted within the trunk 51 to swing pivotally about ahorizontal axis at 58, just forward of a latch hinge connectionrepresented by an angled strap member 59. This is the part normallyabutted resiliently by the keels cushion pad 57. An appropriately biasedcoil compression spring 60 acts against a fixed bottom stop 60 on therear of strap 59, and a tail portion of the pivoted latch arm 56 isconnected to a rod 60 centered in spring 60 and slidable through stop60'; and provision is made for an adjustment of the compression ofspring 60, as by a nut 61 threaded on rod 60" and upwardly abutted bythe spring 60 to urge latch 56 counterclockwise. FIG. 6A shows the keelas normally latched for cruising, and latch 56 releases to enablefinkeel 1 to swing counterclockwise freely (FIG. 6B), should the keelstrike an obstacle or beach in any angular keel setting from fullextension toward or to full retraction. These positions are of coursetaken with the keel in latch.

The operational control of the keel position, over and above theautomatic safety unlatching, is regulated by the adjustment device 23.It comprises an elongated tube 62 which is pivotally connected forwardlyto a bracket ear at the top of angle strap 59 and is threadedly engagedat an aft end thereof by an elongated control rod 63 coaxially movablein the tube. For the purpose the tube 62 is equipped with a nut member64 fixed in its outer end and threadedly engaged by the rod 63. Retainerbearings 65 are welded to the rod on opposite sides of a fixed rotativerod journal bearing 66, which has a pivotal swivel mount at the rear ofand between parallel after-brackets 52. The latter may be MASTCONSTRUCTION As generally shown in FIGS. 7 and 8, the elongated lengthof the mast 8, as molded of fiberglass in a hollow horizontal crosssection (FIG. 9), tapers uniformly from a stepping base (FIG. 7), whichis shaped to have a forward to aft upward bevel 68, to its mainstayedtop. Its width also tapers very mildly from bottom to top, as appears inFIG. 8, and the compounded tapering lowers the center of mast mass tofurther improve the efficiency of the yacht in point of weightdistribution.

Referring to FIG. 9, the mast 8 is of hollow crosssection in a mildlyarced tear-drop outline enclosing a vertically cored space which will ofcourse naturally diminish in area from bottom to top over its extendedlength. Parallel arcuate fiberglass walls 69 of the mast are filled by abalsa core 70, said walls merging aft-wise into a thickened mast bodyportion 69', which is vertically contoured in molding to provide arearwardly slotted space receiving the usual halyard tackle 71. Theleading edge portion 72 of the schematically depicted dacron mainsail isappropriately connected through the masts slot to said tackle; and FIG.9 also shows the oak battens 13 as rivet-secured in a molded fiberglassbatten track member 73 of the sail. The reference numeral 74 designatesthe axis of the wing mast pivot action, now to be described, as about anupright pivot stem which appears in FIGS. 21 and 22.

AERODYNAMIC EFFECTS FIG. 10 is laid out in top plan to schematicallyshow the mast 8 and sail 10 as they affect the laminar air flow on thelee side thereof in a degree to increase the sail drive up to the extentof percent. It also depicts how sail camber may be adjusted fordifferent wind velocities.

Thus, if an apparent wind direction is as indicated by directionalarrows 76 in FIG. 10, and the numerals 77, 78 and 79 are respectivelyconsidered as representing directional orientations of the yacht axis atclose haul, close reach and reach, the numerals 80 represent air flowlines on weather and lee sides of the sail 10 with the mast 8 positionedas indicated in solid line in FIG. 10. The mast set as appears in dottedline in FIG. 10, indicates a camber adjustment (by means shown in FIGS.11-13) for very slow winds. In each case the laminar flow exhibits noturbulence or eddies along the attack zone of the sail, thus affordingthe substantially increased percent sail drive. Such turbulent flow, asindicated at 83, is delayed until the rear marginal portion of sail 10is reached. As depicted in solid line in FIG. 10, the mastsails zeroangle camber adjustment, as at 84, is for normal moderate winds.

Details of the booms yoke gooseneck connection 9 are shown in solid linein FIGS. 11, 12 and 13 in a setting enabling wing mast 8 to pivot on theaxis 74 (FIG. 10). A 45 cambered setting of the gooseneck appears indotted line in FIGS. 11 and 13; and the arrangement to these ends is onehaving very few parts allowing the wing mast to swing automaticallyduring a tack from a normal sailing setting into a predetermined angleof attack, in either of which positions the mast orientation may bemanually set and held, as appears in solid and dotted lines in FIG. 11.

Thus, the forward end of boom 11 has a pivotal mount, on the axis of apin 85 fixed on that end, to an aft cross piece 9 of the generallyrectangular gooseneck yoke 9; and a forward crossbar 9" of the gooseneckcarries certain camber-adjustment details of the improvement.

These include a U-shaped universal pivot strap 86 between the legs ofwhich a slide block 87 is pinconnected to allow gooseneck assembly 9 toswing up and down with the boom. Such motions are typical during sailingmaneuvers. Block 87 has a groove and tongue-type slidable engagementalong an elongated vertical guide strap 88 attached to the forward edgeof mast 8, adjacent the bottom of the latter; and this enables a limitedelevation of boom 11, from a normal sailing position, shown in solidline in FIG. 1, to a raised dotted line position to accommodate thepop-top 3 when the latter is swung upwardly to its dotted line positionand held therein by means to be described.

Again referring to FIGS. 11-13, and in particular FIG. 12, aquasi-circular brake plate 89 is pivotally mounted on a pin axis at 90to a bracket 91, which is specially formed to provide a pair of legsbetween which the bight of the U-shaped pivotal member 86 is received,the bight passing about a rivet or stud 92. An integral upper extension91' of special bracket 91 threadedly receives a stem of a friction stophand knob 93, which stem extends through a brake shoe 94. A part of thatshoe radially overhangs the arcuate upper edge brake plate 89, asappears in FIGS. 12 and 13. Adjacent its lower straight sectored edgethe brake plate 89 is equipped with a channel. formation within whichthe forward cross-piece 9" of gooseneck 11 is rivetsecured.

Thus, when the hand knob 93 and brake shoe 94 are loosened the plate andthe gooseneck yoke may be swung about the formers pivot at 90 and i thenre clamped by threadedly taking up brake shoe 94; and FIGS. 1 1 and 13show such a camber adjustment, to the extent of 45, of swing of thegooseneck 9 from the normal solid line position to the dotted linecamber position. The mast 8 needs swing only 30, as universally coupledto the gooseneck 9 at the slide block 87, strap 86 and stud 92, and asautomatically rotated through the agency of that linkage, when thegooseneck is tilted to the mentioned degree, about the vertical axis ofthe mast stepping means (to be described).

RUDDER OPERATION Structural details of the arrangement for operating therudder assembly 2, as mounted along with its operating control linkage(to be described), from the operative, solid line position of FIG. 1 tothe retracted dotted line position of FIG. 1, are illustrated in FIGS.14-17. A tiller hand grip 95 coaxial with and on the end of an elongatedtiller tube 97 is affixed to a still longer adjusting rod 98 coaxiallydisposed in the tube; and the rod is pin-and-slot connected at 98' to anupper apex portion of a triangular control plate 99. Plate 99 isreceived in an upper aft recess in a molded fiberglass rudder trunk 46;and as appears best in FIGS. 14 and 16, an aft lower apex portion ofplate 99 carries a pin 101 through which an articulation to rudderstructure 2 is in part completed (as will be described); while theforward lower apex portion of plate 99 carries another pin 101', bywhich the plate is pivotally mounted to the remainder of the swingingrudder sub-assembly 2. Spacers 102 are interposed between plate 99 andadjacent wall portions of the rudder trunk recess which houses theplate. The trunk swings for steering about the axis of an upwardly andrearwardly inclined pivot pin 103 at the tail of the hull member I'I.

As thus pivotally mounted in an upper recess of trunk 46, the plate 99has a flat operating rod or link 104 pivoted thereto at its lower apexpin 101, the link 104 extending downward to a point adjacent the bottomaft corner of rudder trunk 46, where it is pivotally connected by athird pin 101" to a vertically adjustable rudder blade proper 105. Trunk46 is recessed at its rear to accommodate a limit vertical position oflink 104 appearing in FIG. 14; and the links rudder connection pin 101"is located adjacent the junction of a quasi-circular upper body portion105 of rudder blade 105 and aft blade tail portion 105". The portion105' is centrally pivoted by a pin 106 in a lower aft recess between theupright walls of trunk 46 and is, like plate 99 and link 104, partiallyhoused within the molded trunk body, the portion 105' projecting onlyslightly from the trunks lower rear corner.

Thus, a pull on the tiller hand grip 95 to rock the triangular line offorce-directing plate 99 counterclockwise (as viewed in FIG. 14) willswing rudder blade part 105" upwardly from its extreme extended downposition shown in solid line in FIG. 14, or an intermediately extendedposition, to the fully retracted, dotted line position of FIG. 14. Thiscontrolled operation is of value in enabling rudder unit 2 to be cleanedof weeds, or to prevent damage thereto while beaching.

FIG. 15 shows the rudder blade-receiving recess as having a plate member105" fixed to a wall thereof, the member presenting a convexly arcuateaft edge. This edge is provided with a pair of arcuately spaced stopnotches or recesses 107, 107 to assist in holding rudder 2 in either ofthe extreme down and up positions depicted in FIG. 14. For this purpose,the rudder is equipped, directly adjacent its link pivot pin '1", whitha double headed stop pin 108, the heads of which ride the outer sides ofthe rudder trunk walls adjacent the bottom of the latter. Pin 108 ismedially encircled by a cylindrical rubber spacer 109 extending betweenthe trunk walls; and as the link 104 elevates from the solid lineposition of FIG. to the dotted line position of that figure, the pin 108travels the arcuate contour of plate 105", departing from a seat in thelower stop notch 107 to a seat in the upper notch 107', and therebyenabling the tiller operator to sense the arrival of the rudder ateither of the positions shown in FIG. 14. Each rudder trunk 46 swingsbodily with its blade 105 about the acutely and upwardly aft-inclinedaxis of its pivot pin connection 103 to the hull member H, with therudder tillers 44 ganged for simultaneous action by crossbar 45 (FIG.3).

MAST STEPPING AND STAYING ward on the axis of the craft and over itsprow from the deck-mounted stepping unit 7. See also FIG. 23. At thistime the temporary side stays 22 are clipped at their bottoms to thechain plates 22.

Now referring to FIGS. 21 and 22, for coaction with the step unit orsub-assembly 7 the mast 8 is equipped at its foot with a fixed metalsocket pad 114 having a I tubular socket portion 115 recessed into themast; which socket part is removably telescoped on a reduced sized stemportion 116 of a swivel or trunnion member 1 17 of unit 7 which is ofinverted T-shape. Oppositely extending arms of member 117 are joumalledin spaced upright furcations of a forked stepping block 118 bolted orotherwise rigidly secured atop the deck panel P, and the furcations areforwardly beveled (FIG. 22) for clearance accommodating the masts swingin being stepped and unstepped.

Trunnion stem 116 has a short key formation 119 at its top which isslidably receivable in a keyway slot formation 120 when oriented crossbeam-wise with the latter; and with the mast oriented in preliminarystepping position A (FIG. 18) the socket 120 and trunnion stem havetheir keyway and key thus oriented for initial telescoped horizontalinterfit when stepping commences. From this position the mast is flippedcounterclockwise on its axis (FIG. 18) to the B" position, in which stemkey 119 laps the end of socket 1 15, thus insuring that the mast willnot slip off the stepping base or block 118 during raising, and alsostabilizing mast 8 in that movement.

Referring to FIG. 23 in conjunction with FIG. 18, with the temporarylower side stays 22 attached between the chain plates 22' and with jibspar 6 extended from its operative, main mast-coupled connection at 6"to a point well forward of the end of mast 8, the spar is employed as animplement to exert an upward push on the mast, thereby swinging thelatter in a vertical plane through dotted line positions, per FIG. 23,to its fully erected dot-dash line position, whereupon the mainstays 21are applied and the temporary stays 22 are dismantled, the mast havingof course re-rotated 90 to its normal fore-aft orientation. Steppingblock stem 116 and mast socket 115 physically represent the axis 74 ofpivotal mast action mentioned at the end of the mast constructiondescription.

JIB SPAR REEF ING DRUM FIGS. 19 and 20 show the jib reefmg drum 5, asappropriately pivoted or rotatably mounted at spar pivot 6' on themid-point of the forestay cross arm 17, to comprise a reel-like body 5having parallel circular line-confining flanges 5", to the uppermost ofwhich a jib spar receiving end 6' is welded. The latter has a hollowoutline in a special elongated elliptical cross section affording acircular socket, as depicted in FIG. 20.

POP-TOP AND TENT Referring to FIGS. 24, 25 and 26, the pop-top and tentunit, as generally designated 3, comprises a generally rectangularhatchway cover 121 pivoted adjacent its forward margin (by means to bedescribed) to the hull deck panel P; and the pre-sewed canvas tentstructure 4 is sustained at its rear when erected by an invertedU-shaped frame 123 of a rod-like nature. Structure 4 includes abox-section tent 122 having side panels 122 joined by a top panel 122",and by preference, an aft fabric panel 124 is equipped with a swingabledoor sub-panel 125. Frame 1235 is suitably mounted removably to thecrafts cabin or hatchway superstructure by inserting its lower legportions 126 in appropriate sockets of the said structure; and snapfastened loops 1 27 marginally connect the tents side top and aft panelsto the frame rod structure 123.

As shown in FIG. 25, the cover 121 of pop-top unit 3 has a pivotalhorizontal mount at 128 to the forward zone of said superstructurethrough the agency of a quadrant-shaped arm 129 welded or otherwiseaffixed at its free end to the inner forward portion of cover 121.Somewhat to the rear of this connection, a pair of supporting andstabilizing links 130 are pivotally connected at 130' to the interior ofcover 121; and the opposite ends of these links each have a pivotal andslidably guided connection, as by means of a shoe 131, to an elongatedfore-to-aft guide rail 132, along which rails the links slide as coverpanel 121 is swung between the solid and dot-dash line positions of FIG.25. Appropriate provisions may be made to releasably latch poptop cover121, in either of the positions appearing in that view, the tent havingbeen stowed beneath the cover.

DISCUSSION A catamaran that relies on beam for stability (beamcatamaran)reaches maximum stability at a small angle of heel, 7 being typical, andthereafter stability decreases rapidly. At 70 there is no stability andthe catamaran will capsize. Hence, designers must use a wide beam toinsure that the catamaran never heels beyond the critical 7 angle. Onthe other hand, the wide beam causes deteriorating performance towindward because of the extra windage, turning ability also deteriorateswith increased beam, and special docking facilities are required forbeamy yachts.

Many drawbacks inherent in the beam-catamaran design can be reduced oreliminated, and the advantages mentioned in the Summary attained, by theinnovation of reducing the beam, eliminating the usual centerboards ineach hull, and adding what is in effect a long ballast-tippedcenterboard between the hulls, which centerboard pivots and hastherefore been referred to as a pivoting fin-keel.

Consider two cruising catamarans 30 feet long, one a beam type and theother a fin-keel type. The fin-keel catamaran is narrow with an overallbeam of 10 feet (l/3 X length) and the beam-catamaran has an overallbeam of feet (l/2 length). The weight of each yacht is proportional tothe surface area, so the beamcatamaran is heavier because its spanningdeck and bridge area is larger. The extra weight inherent in thebeam-catamaran thus becomes an important factor when comparing the two.

If it be assumed for simplicity that the weight of each yacht is onepound per square foot of surface area, the bridge area of the fin-keelcatamaran is then 170 ft and thus it weighs 170 lbs. The bridge area ofthe beamcatamaran is more than twice this area, being 380 square feet,but, because of the nature of its structural design, the weight persquare foot would increase substantially under a realistic criterion, toachieve equivalent structural integrity. Hence, a conservativeweight/ft. estimate would be 2 lbs., and the bridge for thebeam-catamaran would thus weigh 760 lbs.

Each hull would have an area of approximately 330 ft*, and at 1 lb. persq. ft. would weigh 330 lbs. The rigging of each catamaran may beestimated at 100 lbs., and the center of mass at feet above the LWL.

My pivoting fin-keel yacht is designed with a ballast of 1/4 to H3 thehull weight. For contrast 300 lbs. and 600 lbs. will be chosen forexamples. The distance of the center of mass of the fin keel below theLWL is designed at US to l/ 3 the length, and for the present purpose 10feet is arbitrarily chosen.

Using these figures the center of mass of each yacht is calculated usingmoments; it can be arrived at that the center of mass for thebeam-catamaran is located at 3.25 feet above the LWL, 0.14 feetthereabove for the 300 lb. fin-keel catamaran, and 2.3 feet below theLWL for the 600 lb. fin-keel catamaran.

As each catamaran heels at various angles the width of tha beam and thelocation of the center of mass produce restoring forces; and asmentioned above, the restoring moment for the conventionalbeam-catamaran reaches its maximum value at 7". It falls off morequickly than any other yacht, and below zero at beyond which value thecraft will capsize. Therefore, the beam-catamaran must be handled withextreme caution in heavy winds; and when the weather hull lifts the crewmust quickly release the sheets to prevent capsize. Hence abeam-catamaran necessarily sails, under prudent handling, with bothhulls in the water.

By comparison, a plotting of moment values results in a gently risingcurve for the 300 lb. fin-keel catamaran, maximum restoring moment beingat 13 heel, followed by a gentle tapering off. At 100 angle of heelthere is still 40 percent restoring moment left. More dramatic is thecurve for the 600 lb. fin-keel catamaran, which rises quickly; at 100heel angle, percent restoring moment remains. There is no critical windvelocity, barring of course foolish handling in gale force winds whichcould tumble not only a catamaran but a ballasted monohull. These gentlecurves allow the crew adequate time to adjust the sheets so that theangle of heel can be chosen.

Therefore, conceivably with wind velocities of 12-20 mph the crew of the300 lb. fin-keel catamaran could easily sail on one hull. A similarcondition exists for the crew of the 600 lb. fin-keel catamaran withwind velocities of 15-25 mph. By adjusting -the sheets a heeling angleof 15-25 could easily be maintained.

Most of the drag at low speeds is due to skin friction. At medium andhigh speeds skin friction accounts for half of the total drag.Consequently the design trend has been to semicircular hull sectionswhich give the least surface area per unit buoyancy.

Since the beam catamaran necessarily sails with both hulls in the water,the designer assumes the weight is distributed equally between the twohulls when designing for minimum wetted area. A simple analysis can bemade by considering a midsection designed with semicircular hulls,involving considerations such as the buoyancy or volume displaced by thehulls being proportional to the area of the semicircle:

l/2 'n'R or for both hulls:

vrR

The wetted surface is proportional to the circumference of thesemicircle:

l/2 21rR or for both hulls:

Assume the value R l for convenience, then Displacement 1r Wetted Area 2'rr If we now consider one hull as displacing the total weight, thedisplacement of this new hull must be 1r, 5

and to find its radius we equate to the area equation of a semi-circle:

Hence it is concluded that the beam-catamaran has 41 percent plus morewetted surface. Actually, because of the spindle shape of entry and exitthe value is more precisely 35 percent.

Some mention of beam-catamaran centerboard area must be made to makecomplete the comparison of that catamaran and my fin-keel catamaran. Thebeamcatamaran usually has one board in each hull; and the totalcenterboard area for semicircular section hulls is usually 2 percent ofthe sail area. A square feed centerboard area for a 500 ft sail plan istypical.

A comparable fin-keel catamaran may have 50 percent more area (3 percentof the sail area plan), because an exceptionally long centerboard isdesirable. Also the fin-keel will be thicker to have the necessarystrength. While the extra surface area and thicker section may increaseskin friction and wave drag, nevertheless offsetting these disadvantagesare two positive effects: (a) The aspect ratio of the fin-keel will beabout twice that of the centerboards, and thuswill develop more thantwice as much lift for the same amount of drag; and (b) since thefin-keel is positioned in the middle of the bridge superstructure thehulls can be toed out several degrees, thus reducing crab angle dragwhen beating to windward.

In as much as wave interference causes considerable drag when the hullsare spaced too closely, the hull spacing for the tin-keel catamaranshould be the minimum acceptable without introducing excessive drag, inwhich case this effect thus need not be considered as a dynamic factoraffecting cruising.

What is claimed is:

1. A catamaran sailing craft having a fin-keel pivotally mounted on ahorizontal axis adjacent an upper portion thereof to depend between andwell below elongated twin hull members of the craft in a fullydownwardly extended cruising setting of the keel, said hull membersbeing on centers spaced from one an other a distance approximatingone-third of the load water line hull length, the hull members having amildly angled, forwardly divergent toe-out in relation to the centerlineof the craft and being rigidly and permanently inter-connected inlaterally spaced relation to one another by a spanning deck structure,said structure including an upright centerboard trunk mid-way betweenthe hull members in which a pivoted'end of said fin-keel is disposed,said keel being elongated in length, in relation to the length andlateral spacing of the hull members, to an extent also approximatingonethird of the load water line hull length and being weighted adjacentthe keel end, and means for adjustably positioning and maintaining thekeel in selective settings between said fully extended one and a fullyretracted setting in which the keel is housed and directed well aft-wiseof the hull length.

2. The craft of claim 1, in which said positioning and maintaining meansincludes a connection within said trunk to said upper keel portion, andmanually controlled means disposed external of the trunk for operatingsaid connection in adjusting the keel setting.

3. The craft of claim 2, in which said connection comprises an elongatedthreaded rod and nut linkage connected at opposite ends thereof to saidkeel portion and said manually controlled means.

4. The craft of claim 1, and further comprising a releasable latchdevice resiliently holding said keel in any setting thereof, said devicebeing yieldable upon the keels encountering a substantial obstacle toenable the keel to swing aft-ward, independently of said positioning andmaintaining means, about the pivotal keelmounting axis.

5. The craft of claim 2, and further comprising a releasable latchdevice resiliently holding said keel in any setting thereof, said devicebeing yieldable upon the keels encountering a substantial obstacle toenable the keel to swing aft-ward, independently of said position ingand maintaining means, about the pivotal keelmounting axis.

6. The craft of claim 3, and further comprising a releasable latchdevice resiliently holding said keel in any setting thereof, said devicebeing yieldable upon the keels encountering a substantial obstacle toenable the keel to swing aft-ward independently of said positioning andmaintaining means about the pivotal keelmounting axis.

7. A sailing craft having a mast mounted to swing about the axis of anupright step connection to the hull structure of the craft, a sail boom,and a yoke unit articulating the boom to the mast, said unit including agooseneck member mounting said boom and tiltable about a substantiallyhorizontal axis, and a linkage operatively connected between the mastand gooseneck to cause a swing of the former about its said stepconnection axis in response to a tilt of the latter about its saidhorizontal axis.

8. The craft of claim 7, in which said articulating linkage is auniversal type one translating the horizontal axis gooseneck tilt to theupright axis mast swing.

9. The craft of claim 7, in which said step connection includes a swiveldevice enabling the mast to be pivotally lowered and raised in the orderof in an operation of stepping the mast.

10. The craft of claim 7 in the form of a catamaran, in which said stepconnection is located between the crafts twin hulls and includes aswivel device enabling the mast to be pivotally lowered and raised inthe order of 180 in an operation of stepping the mast.

11. The craft of claim 9, in which said swivel device also provides apart at which said mast has its said axis of swing in response to thetilt of the gooseneck.

12. The craft of claim 10, in which said swivel device also provides apart at which said mast has its said axis of swing in response to thetilt of the gooseneck.

13. The craft of claim 7, and further comprising means to secure saidgooseneck in selectively tilted positions.

14. The craft of claim 1, and further comprising a jib mounting sparextending between an elevated point above the. craft and'a cross-memberspanning the space between the hull members, and a jib reel drumrotatably supporting the lower end of said spar on said crossmembermidway of the length of the latter.

15. A catamaran sailing craft having a fin-keel pivotally mounted on ahorizontal axis adjacent an upper portion thereof to depend between andwell below the twin hull members of the craft in a fully extendedcruising setting of the keel, said keel being elongated in length to theextent of substantial fraction of the hull length and being weightedadjacent the keel end, means for adjustably positioning and maintainingthe keel in selective settings between said fully extended one and afully retracted setting in which the keel is directed well aft-wise ofthe hull length, and a rudder unit including a rudder trunk pivotallymounted on the aft end of each of said hull members, a rudder bladepivotally mounted to adjust about a horizontal axis and at leastpartially housed in said trunk, a tiller extending into said trunk, anda linkage also at least partially housed in said trunk and providing adirectionchanging adjustment connection between said tiller and saidblade.

16. The craft of claim 15, in which said rudder trunk has internal meansto releasably hold the rudder blade in a vertically adjusted positionthereof.

17. The craft of claim 1, and further comprising a pop-top and tent unitmounted to swing on a horizontal axis abeam of said hull members, saidunit including a cover member pivotal about said axis and overlaying ahatchway or cabin space of the craft between said hull members when thecover member is in a lowered condition, and a tent attached to saidcover member and shielding said space when the cover member is in araised position.

18. The craft of claim 1, in which said hulls each present an outerfore-to-aft elongated side bulge adjacent and beneath said deckstructure, said bulges extending a substantial portion of the length ofthe hull members and improving the position of the center of buoyancy ofthe craft.

19. A catamaran-type craft having an elongated finkeel mounted to'depend centrally between fixedly and permanently connected, laterallyspaced twin hulls of the craft in a relationship to the normal loadwater line length of said craft and to the lateral spacing of said hullssuch that the effective length of said keel beneath the crafts normalload water level in a fully extended downward position of the keelapproximates onethird of said water line length, and that thelongitudinal centerline. of said hulls are transversely spaced from onea distance also approximating one-third of said water line length.

20. The craft of claim 19, in which said hull centerlines divergeforwardly at a mild angle relative to the longitudinal centerline of thecraft as a whole.

21. The craft of claim 19, in which said fin keel is pivotally mountedon a horizontal axis for upward adjustment from said fully extendedposition toward a more horizontal, retracted position, and vice versa.

22. The craft of claim 20, in which said fin keel is pivotally mountedon a horizontal axis for upward adjustment from said fully extendedposition toward a more horizontal, retracted position, and vice versa.

23. The craft of claim 19, and further comprising a deck structure bywhich said hulls are rigidly and permanently inter-connected inlaterally spaced relation to one another, said hulls each presenting anouter foreto-aft elongated side bulge adjacent and beneath said deckstructure, said bulges extending a substantial portion of the length ofthe hull membersand improving the position of the center of buoyancy ofthe craft.

24. The craft of claim 23, in which said hull centerlines divergeforwardly at a mild angle relative to the longitudinal centerline of thecraft as a whole.

25. The craft of claim 23, in which said fin keel is pivotally mountedon a horizontal axis for upward adjustment from said fully extendedposition toward a more horizontal, retracted position, and vice versa.

1. A catamaran sailing craft having a fin-keel pivotally mounted on ahorizontal axis adjacent an upper portion thereof to depend between andwell below elongated twin hull members of the craft in a fullydownwardly extended cruising setting of the keel, said hull membersbeing on centers spaced from one another a distance approximatingone-third of the load water line hull length, the hull members having amildly angled, forwardly divergent toe-out in relation to the centerlineof the craft and being rigidly and permanently inter-connected inlaterally spaced relation to one another by a spanning deck structure,said structure including an upright centerboard trunk mid-way betweenthe hull members in which a pivoted end of said fin-keel is disposed,said keel being elongated in length, in relation to the length andlateral spacing of the hull members, to an extent also approximatingonethird of the load water line hull length and being weighted adjacentthe keel end, and means for adjustably positioning and maintaining thekeel in selective settings between said fully extended one and a fullyretracted setting in which the keel is housed and directed well aft-wiseof the hull length.
 2. The craft of claim 1, in which said positioningand maintaining means includes a connection within said trunk to saidupper keel portion, and manually controlled means disposed external ofthe trunk for operating said connection in adjusting the keel setting.3. The craft of claim 2, in which said connection comprises an elongatedthreaded rod and nut linkage connected at opposite ends thereof to saidkeel portion and said manually controlled means.
 4. The craft of claim1, and further comprising a releasable latch device resiliently holdingsaid keel in any setting thereof, said device being yieldable upon thekeel''s encountering a substantial obstacle to enable the keel to swingaft-ward, independently of said positioning and maintaining means, aboutthe pivotal keel-mounting axis.
 5. The craft of claim 2, and furthercomprising a releasable latch device resiliently holding said keel inany setting thereof, said device being yieldable upon the keel''sencountering a substantial obstacle to enable the keel to swingaft-ward, independently of said positioning and maintaining means, aboutthe pivotal keel-mounting axis.
 6. The craft of claim 3, and furthercomprising a releasable latch device resiliently holding said keel inany setting thereof, said device being yieldable upon the keel''sencountering a substantial obstacle to enable the keel to swing aft-wardindependently of said positioning and maintaining means about thepivotal keel-mounting axis.
 7. A sailing craft having a mast mounted toswing about the axis of an upright step connection to the hull structureof the craft, a sail boom, and a yoke unit articulating the boom to themast, said unit including a gooseneck member mounting said boom andtiltable about a substantially horizontal axis, and a linkageoperatively connected between the mast and gooseneck to cause a swing Ofthe former about its said step connection axis in response to a tilt ofthe latter about its said horizontal axis.
 8. The craft of claim 7, inwhich said articulating linkage is a universal type one translating thehorizontal axis gooseneck tilt to the upright axis mast swing.
 9. Thecraft of claim 7, in which said step connection includes a swivel deviceenabling the mast to be pivotally lowered and raised in the order of180* in an operation of stepping the mast.
 10. The craft of claim 7 inthe form of a catamaran, in which said step connection is locatedbetween the craft''s twin hulls and includes a swivel device enablingthe mast to be pivotally lowered and raised in the order of 180* in anoperation of stepping the mast.
 11. The craft of claim 9, in which saidswivel device also provides a part at which said mast has its said axisof swing in response to the tilt of the gooseneck.
 12. The craft ofclaim 10, in which said swivel device also provides a part at which saidmast has its said axis of swing in response to the tilt of thegooseneck.
 13. The craft of claim 7, and further comprising means tosecure said gooseneck in selectively tilted positions.
 14. The craft ofclaim 1, and further comprising a jib mounting spar extending between anelevated point above the craft and a cross-member spanning the spacebetween the hull members, and a jib reel drum rotatably supporting thelower end of said spar on said cross-member midway of the length of thelatter.
 15. A catamaran sailing craft having a fin-keel pivotallymounted on a horizontal axis adjacent an upper portion thereof to dependbetween and well below the twin hull members of the craft in a fullyextended cruising setting of the keel, said keel being elongated inlength to the extent of substantial fraction of the hull length andbeing weighted adjacent the keel end, means for adjustably positioningand maintaining the keel in selective settings between said fullyextended one and a fully retracted setting in which the keel is directedwell aft-wise of the hull length, and a rudder unit including a ruddertrunk pivotally mounted on the aft end of each of said hull members, arudder blade pivotally mounted to adjust about a horizontal axis and atleast partially housed in said trunk, a tiller extending into saidtrunk, and a linkage also at least partially housed in said trunk andproviding a direction-changing adjustment connection between said tillerand said blade.
 16. The craft of claim 15, in which said rudder trunkhas internal means to releasably hold the rudder blade in a verticallyadjusted position thereof.
 17. The craft of claim 1, and furthercomprising a pop-top and tent unit mounted to swing on a horizontal axisabeam of said hull members, said unit including a cover member pivotalabout said axis and overlaying a hatchway or cabin space of the craftbetween said hull members when the cover member is in a loweredcondition, and a tent attached to said cover member and shielding saidspace when the cover member is in a raised position.
 18. The craft ofclaim 1, in which said hulls each present an outer fore-to-aft elongatedside bulge adjacent and beneath said deck structure, said bulgesextending a substantial portion of the length of the hull members andimproving the position of the center of buoyancy of the craft.
 19. Acatamaran-type craft having an elongated fin-keel mounted to dependcentrally between fixedly and permanently connected, laterally spacedtwin hulls of the craft in a relationship to the normal load water linelength of said craft and to the lateral spacing of said hulls such thatthe effective length of said keel beneath the craft''s normal load waterlevel in a fully extended downward position of the keel approximatesone-third of said water line length, and that the longitudinalcenterline of said hulls are transversely spaced from one a distancealso approximating one-third of said water line length.
 20. The crafT ofclaim 19, in which said hull centerlines diverge forwardly at a mildangle relative to the longitudinal centerline of the craft as a whole.21. The craft of claim 19, in which said fin keel is pivotally mountedon a horizontal axis for upward adjustment from said fully extendedposition toward a more horizontal, retracted position, and vice versa.22. The craft of claim 20, in which said fin keel is pivotally mountedon a horizontal axis for upward adjustment from said fully extendedposition toward a more horizontal, retracted position, and vice versa.23. The craft of claim 19, and further comprising a deck structure bywhich said hulls are rigidly and permanently inter-connected inlaterally spaced relation to one another, said hulls each presenting anouter fore-to-aft elongated side bulge adjacent and beneath said deckstructure, said bulges extending a substantial portion of the length ofthe hull members and improving the position of the center of buoyancy ofthe craft.
 24. The craft of claim 23, in which said hull centerlinesdiverge forwardly at a mild angle relative to the longitudinalcenterline of the craft as a whole.
 25. The craft of claim 23, in whichsaid fin keel is pivotally mounted on a horizontal axis for upwardadjustment from said fully extended position toward a more horizontal,retracted position, and vice versa.